Men are frustrated by how unfairly the justice system defers to women. My peer group isn't quite at the stage where divorce is a common reality, but even now some are worried any future custody battle will favour wives and they'll lose their kids. The courts, they say, are biased. I think they're correct, but their frustration is usually fired at feminists or a magical all-powerful group of women conspiring to undermine the male status quo. But I have to ask: really? A girl did this to you?
Custody and family legal matters appear unfair because males set it up like this. The concept revolves around women being seen as more nurturing, default mothers who should be protected with extraordinary care. This is now baked into the legal system from top to bottom. Of course, this is unfair, but it doesn't fit neatly into right or wrong either. That's just how the legal system was structured. So when men complain, they have to remember god/aliens didn't create the justice system. It was them.
I don't think anyone disagrees about the once clear and particular societal roles for both men and women, which stayed pretty much intact for centuries. None of that was controversial until the suffragette/feminist movement told us it was time for a change. Everyone - including women - assumed women were weaker and needed extra protection from the state. It was assumed men were stronger and didn't need as much protection. It was assumed women would always become mothers. It was assumed men wouldn't prioritise child-rearing over working at a job because it wasn't their role.
The justice system was built for this. Again, it's not a bad or a good thing, it's simply the way things used to be. Now it's changing as men desire more child custody or more familial protection in court. They're complaining as they discover at the sharp end of a gavel that the system it was set up precisely for the opposite world they now desire. I think this is what feminists mean when they speak so impossibly of the patriarchy.
But this isn't feminism's fault - women didn't create the justice system. If men now want changes, they should reassess the default assumptions baked into some of our most stalwart institutions and figure out what might need to change as we evolve into a more equal world. However, none of that will be possible if we fail to understand how and for what purpose those institutions were constructed in the first place.
Although, forgetting an institution's purpose and remembering how to maintain it is the connecting thread explaining most of today's societal ills. So I don't have a lot of faith.